In U.S. Pat. No. 3,883,333, a process is described for producing a needled glass strand mat in which continuous glass strands are laid down on a moving conveyor from a plurality of feeders which are traversed across the width of the conveyor. The mat after its formation on the conveyor is passed through a needler to impart mechanical integrity to the mat by puncturing the strand mat with a multiplicity of rapidly reciprocating barbed needles. The mat leaving the needling machine is trimmed at its edges to provide a definite width of mat of given density. Mat prepared in the manner shown in this prior art process has found particular utility in the preparation of stampable, fiber glass reinforced, thermoplastic resin sheets.
In the manufacture of continuous glass strand mat as shown in this process, it is found that the edges of the mat laid down on the conveyor tend to be irregular and of lower density than the major surfaces of the mat on the conveyor. In providing a finished mat of a given width having a uniform density, it is ncessary to trim the mat as it leaves the needler, a procedure which reduces the efficiency of the process to a significant degree since the trim represents waste product. The reciprocating needler also contributes to the reduced efficiency of the process since the mat edges are forced outwardly from the mat path of travel as the needler strikes the mat on its downward stroke during its passage through the needling zone. This action in the needling zone causes the edges of the mat to become thinner than the main body of the mat and these edges must be trimmed away from useful, uniform density mat emerging from the needler.